Spoilers of 'The Big Bang Theory' suggest that Leonard (Johnny Galecki) and Penny's (Kaley Cuoco-Sweeting) honey moon may be very short-lived even if the duo succeeds in reaching that point in their life. It is expected that an allegation from Leonardo's past will appear in 'Big Bang Theory' Season 9 episode 2.

Quoting a report in TV Line, IB Times states that Melissa Tang has been cast as Mandy, the woman whom Leonard kissed while on a North Sea expedition. Leonard told Penny about this just before the couple left for Las Vegas to get married toward the end of Season 8.

Earlier, Tang also featured in 'Mom,' 'How I Met Your Mother,' and 'New Girl.'

In 'The Big Bang Theory' Season 8 finale, Leonard confessed to kissing a woman because he wanted to go into their marriage with no secrets. However, Penny was concerned that he was trying to disrupt their wedding plans. Now it remains to be seen if the couple will finally get married in Season 9 or will Penny refuse to go forward with it, as Leonard has been unfaithful.

It is expected that 'The Big Bang Theory' Season 9 will also be packed with drama for Sheldon (Jim Parsons) and Amy (Mayim Bialik). Viewers last saw Amy when she requested that they spend some time away from each other with a view to reassess their relationship. Later, it was revealed in the Season 8 finale that Sheldon had a ring and was on the verge of proposing to Amy to marry him. However, this did not happen.

Last month, 'The Big Bang Theory' executive producer and writer Steven Molaro revealed that in the opening episode of the upcoming season, fans will come to know when Sheldon bought the ring. In addition, the new season will also reveal a lot about Amy's family and her past.

'The Big Bang Theory' Season 9 will premiere at 8 p.m. EDT on Sept. 21 on CBS.