Article continues below advertisementSerena Williams' support for her sister Venus comes with a price.During the Wednesday, January 28, episode of TODAY With Jenna & Sheinelle, Serena, 44, joked about serving as a notary in her sibling's marriage to Andrea Preti.Article continues below advertisementSource: TODAY With Jenna & Sheinelle/YouTubeSerena Williams guest-starred on 'TODAY With Jenna & Sheinelle.'Serena expressed how it was "so special" and "emotional" cheering Venus, 45, on - and serving as a witness to her signing legal marriage documents.