Labour peer Lord Waheed Alli committed four minor breaches in his register of interests, a report has found.
The breaches are not related to previous revelations that Lord Alli paid for clothes for senior Labour figures, including Sir Keir Starmer, and allowed some of them to use his properties.
A House of Lords standards commissioner recommended Lord Alli apologise for failing to properly register his interests in a series of businesses and a charitable foundation.
In his apology letter to the Chair of the House of Lords Conduct Committee, the peer accepted the findings and vowed to "endeavour to follow the Code of Conduct at all times to prevent this from happening again".
A complaint triggered an investigation into Labour donor Lord Alli, who was already facing scrutiny over his donations of clothes to senior politicians.
A report by the House of Lords Standards Commissioner found that Lord Alli improperly removed his controlling stake in Silvergate BP Bidco Limited, the media company behind CBeebies show Peter Rabbit, from the register.
Lord Alli sold part of the company to a Hollywood studio in 2019 and no longer benefited financially from his shares, but still maintained a controlling stake in the firm.
The commissioner found Lord Alli also failed to register that he was an unremunerated director of a firm in the British Virgin Islands tax-haven in time.
Lord Alli correctly registered his trusteeship of The Charlie Parsons Foundation but should also have included his position as an unremunerated director of the foundation, the commissioner found.
Lord Alli co-founded the charity, which focuses on investing in "new talent, new projects, and new business ideas" in the TV and entertainment industry.
In the report, the commissioner said: "While I consider each individual breach of the Code to be minor, I have found there to be four breaches in total, and have therefore recommended that Lord Alli write a letter of apology."
In his letter to Conduct Committee chair Baroness Manningham-Buller, Lord Alli said: "I am writing to you today to offer my apology for my breach of conduct by not registering my interests correctly.
"I will endeavour to keep to the Code of Conduct at all times to avoid such circumstances again."