Shrutvaa tu aham ayodhyaayaam
vivaaha artham tava aatmajaan
Mithilaam upayaataan tu
tvayaa saha mahiipate
tvarayaa abhupayaato aham
drasht`u kaamaha svasuhu sutam.
Yudhaajit was the Uncle of Bharata and brother of Kaikeeyi. He wanted to take Bharata to his Keekaya kingdom. When he went to Ayodhya, he came to know that Dasaratha took Bharata to Mithila for Bharata's marriage. Yudhajit immediately rushed to Mithila and meets Dasaratha. The above verse is his words.
Why did not Dasaratha invite Yudhaajit for the marriage of his nephew? This is an elementary courtesy. Was Dasaratha entering into any secret pact with Janaka, the details of which Yudhaajit should not know?